Some recent models of liquid crystal displays and like display panels include a parallax barrier so that the viewer can see (autostereoscopic) 3D images without using a filter system or other visual effect enhancer. The parallax barrier contains stripes of optically transparent regions and opaque regions.
A man's eyes sit spatially apart on the head. So the eyes receive images as seen from two different points in the normal field of vision. The brain then exploits parallax of these two images to perceive it in three dimensions. A three-dimensional (3D) display is produced based on the same principle, i.e., a parallax experienced by the viewer's right/left eyes viewing images produced as seen from different points.
In a 3D display device with a parallax barrier, a parallax barrier 102 outside a display panel 101 sets a particular viewing angle (see FIG. 7) for a right eye image and a left eye image produced by the display panel 101. The eyes receive respective images when the viewer positions himself in a particular viewing region in space, so that the viewer can perceive a 3D image (see FIG. 8).
This kind of 3D display device including the combination of a parallax barrier and a display panel is disclosed, for example, in Japanese Laid-open Patent Application No. 3-119889/1991 (“Tokukaihei No. 3-119889,” published on May 22, 1991). In the 3D display device of Tokukaihei No. 3-119889, the parallax barrier is included in a switching liquid crystal layer. Turning on/off the barrier pattern in the switching liquid crystal layer enables/disables parallax barrier effect. This enabling/disabling switches the device between 3D mode and 2D mode.
The combination of a parallax barrier and a display panel is applicable in a display device for other purposes than the 3D display (see FIG. 9(a)). The combination could be used, for example, to produce different displays to different viewers (“dual image display;” see FIG. 9(b)).
Theoretically, the dual image display is produced based on the same image separation as 3D displays. However, new problems, which were not found with 3D display devices, occur in the actual manufacture of display devices producing a dual image display. Specific description of the problems will be given next.
A comparison of FIGS. 9(a), 9(b) would clearly show that the display images are separated by the parallax barrier at the same points for a 3D display and for a dual image display. Some conditions (for example, distance between the viewing points) concerning the viewing points, however, differ greatly between the two display modes.
More specifically, in 3D display mode, the distance between the viewing points is equal to the distance between the viewer's eyes. In contrast, the distance between the viewing points in dual image display mode needs be greater than that in 3D display mode so that viewers can position themselves away from each other. The distance between the viewing points can be set to a given value by varying the distance between the color filter and the parallax barrier.
The distance, D, between the viewer and the display screen is given by:D=ES/nP  (1)where E is the distance between the viewing points in millimeters, P is the pixel pitch of the color filter in millimeters, S is the distance between the color filter and the parallax barrier in millimeters, and n is the refractive index of a medium between the color filter and the parallax barrier.
Assume E=62 mm, D=600 mm, and P=0.1 mm for a 3D display. Assume also that the medium between the color filter and the parallax barrier be a glass substrate and a glass's refractive index n=1.52. Inserting these values to equation (1), we obtain a distance S between the color filter and the parallax barrier at S=1.47 mm. This value of distance S is perfectly feasible even with the glass substrate intervening between the color filter and the parallax barrier. The provision of the parallax barrier outside the display panel poses no problems at all in the 3D display device.
Now, assume E=900 mm for a dual image display. All the other conditions are identical to the 3D display. Inserting the values to equation (1), we obtain S=0.1 mm. This value of distance S is extremely difficult to achieve if there is a glass substrate intervening between the color filter and the parallax barrier. In other words, the color filter is required to be closer (about 50 μm to 100 μm) to the parallax barrier in the dual image display device than in the 3D display device. This requirement, unlike in the 3D display device, makes it extremely difficult to provide the parallax barrier outside the display panel in manufacture.